Display devices including active matrix substrates in each of which a switching element is provided for each pixel are in wide use. Active matrix substrates including thin film transistors (hereinafter referred to as “TFTs”) as switching elements are called TFT substrates. In this description, portions of a TFT substrate that correspond to pixels of a display device may also be referred to as pixels. Using an oxide semiconductor, instead of amorphous silicon or polycrystalline silicon, as a material for an active layer of a TFT is also proposed.
An active matrix substrate typically includes a TFT, a pixel electrode, a source wire connected to a source electrode of the TFT, and a gate wire connected to a gate electrode of the TFT. When such an active matrix substrate is used in a display device having a touch sensor function (hereinafter referred to as an “in-cell touch panel display device”), the active matrix substrate may be provided with a detection electrode of a touch sensor (e.g., PTL 1).
The active matrix substrate is also provided with a pixel contact portion that connects the pixel electrode and a drain electrode of the TFT to each other, a terminal portion for connecting the source or gate wire and an external wire to each other, etc. In this description, portions that connect two conductive layers together, such as the pixel contact portion and the terminal portion, are collectively referred to as “connecting portions”.
In such a connecting portion, for example, an upper conductive film is disposed so as to be in contact with a lower conductive film in a contact hole formed in an insulating layer. For example, PTL 2 discloses a pixel contact portion having such a connection structure. This structure is disadvantageous in that when the contact hole is deep, the upper conductive film may provide low coverage to cause breaking.
FIG. 13 is a schematic sectional view illustrating a connecting portion that has undergone breaking. An upper conductive film 98 is disposed so as to be in contact with a lower conductive film 92 in a contact hole 96p formed in an insulating layer 96. The upper conductive film 98 tends to be thinner on the side wall of the contact hole 96p than in the vicinity of an opening of the contact hole 96p. Thus, depending on the depth and the shape of the contact hole 96p, breaking of the upper conductive film 98 may occur on the side wall of the contact hole 96p, as shown in the figure, resulting in electrical disconnection with the lower conductive film 92 or higher contact resistance.
PTL 3 proposes forming a conductive material film on the side wall of a contact hole by an etch back process in order to suppress the increase in contact resistance. An upper conductive film is disposed so as to be in contact with the conductive material film on the side wall of the contact hole and with a lower conductive film at the bottom of the contact hole.